The proposed work deals with the timing and interrelationships of the age of onset of the expression of fear in human infants exposed to four potentially threatening situations: the deep side of the visual cliff, the approach of a stranger, the departure of the mother, and optical expansion patterns which can specify imminent collision. Data from our lab and those of others suggests that a major developmental shift takes place in reactions to threatening (as opposed to actually painful) stimuli between six and nine months of age. By studying the relationship of the age of onset of these various fears, and relating them to measures of cognitive development, experience, and (possibly) temperamental variables, we hope to construct a model of the mechanism underlying the early development of fear in the human infant.